Means for cooling the windows of acceleration tubes for electrostatic generators



Jan. 14, 1958 D. M. ROBINSON 2,820,165

MEANS FOR COOLING THE wmnows OF ACCELERATION TUBES FOR ELECTROSTATICGENERATORS Original Filed July 13, 1951 2 Sheets-Sheet 1 Jan. 14, 1958D. M. ROBINSON- 2,820,165

MEANS FOR COOLING THE WINDOWS 0F ACCELERATION TUBES FOR ELECTROSTATICGENERATORS Original Filed July 13, 195] 2 Sheets-Sheet 2 I N V EN TOR.lierzzis'JtCB03bas'an 2M BMW/m a) MEANS FOR COOLING THE WINDOWS FACCEL-' ERATION TUBES; FOR' ELECTROSTATIC GEN? ERATORS Denis- M.Rohinson,,-Arlington, Mass.,-- assignor to High Voltage EngineeringCorporation, Cambridge, Mass,

a corporation of Massachusetts Original application July-13, 1951,Serial No; 236,652,

now Patent No.-2,729','748,. datedJanuary 3, 1956. Divided ,and thisapplication September 9, 1953, Serial No. 379,258

3 Claims. (Cl. 31335) This application. is a division of my co-pendingapplica' tion Serial No. 236,652; filed July 13, 1951, now.Patent No;2,729,748, and is directed to subject matter required to .be divided outon March 31, 1952, because directed to an electric lamp discharge devicewith temperature mod ifying. means.

This invention relates to apparatus for sterilizingfoods,.

drugs and other materials or substances, or causing desirable chemicalchanges in material by ionizing radiations. More particularly it relatesto the irradiation with.

resulting sterilization of such materials by the action of an electronbeam of extremely high energy. ,It is shown in connection withmeanstoeffect irradiationin such manner as rapidly ;to scan such materials,with'a high,

intensity beam so as to increase the instantaneous ionization density,and thereby reduce possible adverse effect on the taste, color,nutritive value, potency or other required properties of such materials.

The present invention utilizes and is applicable to anyconcentratedhigh-energy stream of electrons. Therefore,

while I have in the drawings illustrated though more or lessdiagrammatically certain forms of parts of theVan or magnetic fieldbefore the high intensity beam issues through the window of theacceleration tube, in which case the window is much elongated in thedirection of travel of said .-high -intensity electron beam in itsscanning action. Such-a window constitutes or is formed as a long narrowslot'covered by thin aluminum foil, and provision is made as hereindisclosedfor carrying away the heat generated by thepassage of theelectron beam through the window.

This is eifectedmore readily than if the same electronbeam-were'continuously passing, with resultant intense.

heatingthrough the same small window area, instead of being moved backand forth along such narrow slot.

I herein .broadly claim the provision of means for cooling the elongatedwindow.

I believe that an extremely intense ionization at a given point and at agiveninstant of time results in more efiective sterilization. Theresults of my invention-are accomplished by producing intense ionization,by continuous electronbeams which are made possible as a result of theVangde Graafi-High Voltage'Engineering Corporation n que I have statedthat the objective. in the sterilizationof foodsand drugsis to inactivecertain organisms without,

however, ,produci ng' undesirable. changes of taste or changes innut'ritive or medicinalqualities. This,.I have atent ascertained, isbest achieved when the lowest possible ionic "eifects'result from theapplication of the-required sterilization dose.

Furthermore, my investigations show'that when sub in accordancewith myinvention, many changes in taste or nutritive or medicinal qualities maybe prevented: Not

only may changes in taste and potency actually be 're-' duced, but theirradiation dose requirements are at the Sametime actually reduced onsome, at least, of the organisms presentin the material and substancessubjected to the sterilization action of an electron beam of extremeintensity.

Hav-ingthus'set forth the objects of my invention and the general naturethereof, 1 will now disclose certain embodiments of means or apparatusby which 'I may practice my invention.

In the accompanying drawings:

Figi-l is adiagram, mainly in longitudinal section, illustrating themodification or change in position of the axis of an electron beam ofextreme intensity after issuing as an approximately parallel beam fromthe lower end of the'acceleration tube of one form of a Van de Graaffelectrostatic generator somewhat diagrammatically shown, suchmodification or change in position of the axis .of the beam occurring atextreme speed, as, for example, by oscillating such beam at a speed, ofone thousand times a second or less, or more, by the actionofalternating current electromagnets, that is, with the scanning-occurringparallel to the plane of the said electromagnet coils,.the'

said electron beam being focused or given the desired convergence withinthe acceleration tube by a surrounding wise a widely flaring or flaredlower end to providespace,

wherein the scanning action of a field occurs through the action of apair of alternating current electromagnets, be

fore the electron beam issues through the window, which.

therefore is greatly elongated in the direction of the scanning movementof the electron beam,

Fig. 3 is a diagrammatic detail in side elevation and,

vertical section of the lower portion of an acceleration, tube of anydesired type, but having a flaring or flared.

lower end terminating in an elongated narrow window and representingcooling means for such window;

Fig. 4 is a bottom plan view of the elongated narrow window representedin Fig. 2;

Fig. 5 is a diagrammatic view of the lower end of an acceleration tubeof any type, provided with means to cool a window at or near the lowerend thereof; and

Fig. 6 is a side elevation, but partly in vertical section,

of the lower end of the form of acceleration-tube shown in Fig. 1.

Referring more particularly to the drawings, and first to Fig. 1thereof, a small portion, broken away, of one form or type of theacceleration tube of a Van de Graaff electrostatic generator, but to theuse of whichv my invention is not limited, is indicated at 1. The said.generator is capable of producing a narrow beam of high: speedelectrons, the energy whereof is or may beon theorder of several millionvolts and as much .as five million or more volts, and is manufactured byHigh Voltage Engineering Corporation.

The high speed electron beam emanatingfrom, the,

cathode of the acceleration tube .1 is indicatedat; 2. The

electrons of the. bea nZ are, accelerated throughthep,

vacuum region of the acceleration tube 1 in a manner not necessary toexplain herein in detail, and in the construction shown in Fig. 1 theytravel in a straight line or path and issue through the window 3 at thelower end thereof, having been focused by the focusing magnet indicatedat 311 in Fig. 1.

Still referring to Fig. 1, at the proper distance below the window 3 ofthe acceleration tube 1 is provided a suitable support 4 which may bestationary or which, as is here the case, may be a conveyor such as abelt that is driven at a suitable speed forward, transversely to thedirection of the axis of the electron beam 2. This motion is indicatedas being to the left, as indicated by the arrow. While the said support4 may be positioned at any suitable distance below the window 3 in theconstruction shown in Fig. l, I represent it as positioned at a distanceof fifteen to forty centimeters therefrom, but as an electron beamsscatters somewhat while passing through the air, I may reduce the lengthof the air path as much as possible, so that the material or product isalmost in contact with the window 3.

I am aware that scattering always occurs in the window of anacceleration tube through which the electrons emerge. There is alsoscattering in any air path or gas path through which the electrons mustpass on their way to the product on the conveyor belt or other support,and finally there will be very considerable scattering in the productitself. All of this is primarily elastic nuclear scattering.

The scattering in a gas is proportional to the square of the atomicnumber. Thus hydrogen or helium would scatter very much less than airand would be a preferred gas between the windows in Fig. 5, yet to bedescribed.

The present invention and other related inventions assigned to HighVoltage Engineering Corporation are based upon fundmental work done bythe scientific group associated with the said High Voltage EngineeringCorporation.

When the scanning action is above the window of the electron tube, as inFig. 2 yet to be described, the product is below and close to thewindow, as will be more specifically referred to herein.

The product, material or substance to be sterilized is represented at 5,but because of space limitations is merely diagrammatically shown.

While not herein claimed, I provide means for scanning, moving to andfro, or sweeping the electron beam 2 at an extremely high speed, as forexample, at a speed of 1,000 oscillations per second, and even more incertain cases. A high scanning frequency is necessary in order thatuniformity of irradiation, particularly in the regions of the productnear the surface, may be achieved. This scanning, moving to and fro, orsweeping of the electron beam may be in any suitable or satisfactorymanner. In Fig. 1, I have indicated for the purpose the creation of amagnetic field directed at right angles to the direction of propagationof the electron beam 2. This will cause the deflection of the electronbeam 2 in a direction at right angles both to the normal path of theelectron beam 2 and to the direction of the magnetic field, with anamplitude of oscillation depending upon the energy of the electrons andthe intensity of the magnetic field. It may be small or may be fiftydegrees, sixty degrees or even ninety degrees.

In the construction shown in Fig. 1 there are provided twoalternating-current magnetic coils or magnets 6, 7. The axis ofthealternating-current magnetic field is indicated by the line 8. Theextent of spread, sweep or scanning movement of the electron beam 2 isindicated by two lines 9, 10. In Fig. l the angle of scan is representedas about fifty degrees. The electron beam 2 is scanned in a directionparallel to the plane of said magnetic coils '6, 7.

The magnetic field is created by an alternating current passing throughthe said magnetic coils 6, 7. The electron beam will oscillate; that is,it will be given its scan ning movements about its normal beam positionwith a frequency which is that of the oscillating current, and with anamplitude of oscillation depending upon the strength of the magneticfield, which may be varied as desired. The location of the magneticcoils or magnets 6, 7 is shown merely diagrammatically and in actionthey give the desired deflection of the electron beam 2. Any extent ofangular displacement of the electron beam 2 in the vicinity ofthemagnetic field will cause a lateral movement of the center of theelectron beam on the product 5, the magnitude of which depends, asstated, upon the strength of the magnetic field and also on the distanceof the product 5 on the support 4 from the magnetic field. One or moremagnetic coils may be used to accomplish the desired purpose.

In Fig. 2, and in side elevation in Fig. 6, is represented the lower endportion of a late type or model of acceleration tube of a Van de Graatfelectrostatic generator and which acceleration tube may be otherwisesimilar to that shown in Fig. l, excepting that the lower end of saidacceleration tube is shown as markedly outwardly flared or flaring at 21to left and to right in said Fig. 2 that is, in two opposite directionsso as in one direction to be in cross section of greatly elongatedlength as indicated, but the width of which flaring portion is about thesame as the normal diameter of said acceleration tube above the flaringportion, or it may be less. The said flaring portion 21 terminates atits extreme lower end in a window 22, which is a long narrow slot and iscovered by a thin aluminum foil 20. Such window must support atmosphericpressure on the outside with vacuum on the inside. The narrowness of theslot and the support given by the closely spaced long sides of the frameinsure this.

The length of the said window 22 is preferably such that I may impart tothe electron beam within said flaring portion 21 a scanning or sweepingmotion extending through fifty degrees or more, and if desired as muchas ninety degrees. For that purpose I employ magnetic coils 23, 24, suchas shown at 6, 7 in Fig. l, or I may employ suitably shaped electrodes,and I preferably make said magnetic coils or conducting plates smallenough to position them suitably within the flaring portion 21. Thisgives close coupling with the electron beam and accordingly reduces thescanning power required. Also the material of the vacuum wall thusserves as a shield against stray external fields.

However, I may, as shown in Figs. 2 and 6, provide the magneticdeflection by placing magnetic coils 23, 24, or parallel conductingplates, entirely outside the vacuum chamber of the acceleration tube.

Preferably the side walls constituting the flaring lower end of theacceleration tube are made of some nonmagnetic material for example,aluminum and the magnetic coils 23, 24 are brought as close as possibleto the two opposing faces of the flaring lower end 21 of theacceleration tube 1. In order to reduce eddy current loss in the sidewalls 26 of the said flaring lower end portion of the acceleration tube1, the section or portion of the acceleration tube subject to themagnetic flux may be made of some plastic material so attached as to bevacuum-tight. So long as the electron beam is passing through themagnetic field, the deflection of the electron beam from its originaldirection continues to increase. After emerging from that field theelectron beam continues in a straight path which is a prolongation ofits path at the point of leaving the magnetic field. In order to obtainthe desired efiect without large coils or iron cores, I prefer to have arelatively weak magnetic system and, therefore, I allow the electronbeam a path-length within the magnetic field sufficient to produce therequired deflection. With such arrangement it is perfectly possible tohave an angle of scan of fifty degrees or even ninety degrees within theflaring end portion 21 of the acceleration tube 1.

In the just described construction or arrangement the conveyor belt,indicated at 25 and in said Figs. 2 and 6, is positioned close below thewindow 22 which is at the extreme lower edge of the said flaring portion21.

By causing the scanning action to take place within the said flaringlower end portion 21 of the acceleration tube,

it is effected therefore before any scattering has taken place, andtherefore the electron beam is thus acted upon while the electron opticsare still rigid. It is pertinent here to point out that the electronoptics of the Van de Graaff type of acceleration tube constant-potentialaccelerators are very favorable and indeed compare in kind with theprecision of the electron microscope, with which, however, my inventionhas nothing to do.

As already set forth, the scanning action may be applied before theelectron beam issues through the window 22 of the acceleration tube, asillustrated in Figs. 2, 4 and 6. In such case the window 22 must be longin the direction of the scanning movement of the electron beam, and ittherefore is a long narrow slot covered by a thin aluminum foil. Such awindow is advantageous also, as already indicated, in that it carriesaway the heat generated by the passage of the electron beam through it,more readily than if the electron beam were continuously passing throughthe same small area. The flow of a generated heat can be furtherincreased by having the frame of the window 22 made of material of goodheat conductivity, or it may be liquid cooled. The narrowness of theslot-like window 22 and the support given by the closely spaced longsides of the frame at the extreme lower flaring end 21 of theacceleration tube I assure that the window will support atmosphericpressure on the outside with a vacuum inside.

In addition, and whether the window has the shape of a long slot as setforth with respect to Figs. 2, 4 and 6, or whether it be substantiallycircular in cross section as may be the case in the construction shownin Fig. 1, I may, and desirably do, provide means other than the shapeor structure of the window and its frame for cooling the window, as byscouring the atmospheric surface thereof with a blast of gas or withfine sprays of liquid or solid materials.

In Figs. 3 and 5 I have represented one means for the purpose, Fig. 5showing such means applied to the lower end of an acceleration tube, theentire tube being of circular or substantially circular cross section,and Fig. 3 showing the same or similar means applied to the lowerflaring end of the acceleration tube shaped as illustrated in Figs. 2and 6.

In both Figs. 3 and 5 the lower end portion of an acceleration tube of aVan de Graafi or other type is diagrammatically indicated at 27.

Referring to Fig. 5, at a suitable distance above the extreme lower endof the acceleration tube 27 is provided an aluminum window 28 and at theextreme lower end of the said tube 27 is provided a very thin window 29,preferably thin aluminum foil, as for the previously described windows 3and 22. The space between the two windows 28, 29 is filled preferablywith helium as at atmospheric pressure. Supported suitably outside theacceleration tube 27 is a pump 31 connected at its intake side by a pipe32 with the helium chamber 30 and at its output side also connected withthe said helium chamber by a pipe 33 terminating in a jet-formingorifice 34, by which the helium gas is forcibly discharged by the pump31 against the lower surface of the aluminum window 28. The gas can becooled by suitable cooling coils or heat interchanger before beingdischarged against the window. The electron beam is showndiagrammatically by the arrow 35.

Having thus disclosed several illustrative embodiments of apparatus forpracticing my invention, it is to be understood that although specificterms are employed, they are used in a generic and descriptive sense,and not for purposes of limitation, the scope of the invention being setforth in the following claims.

I claim:

1. A high-vacuum acceleration tube having means at one end portion forcreating a beam of high-energy electrons for passage along said tube, afinal electron-permeable exit window and another electron-permeablewindow spaced from and anterior to the said final electronpermeable exitwindow, the space between said windows being adapted to be filled with agas, and a pump having an intake passage and a discharge passage, bothsaid passages being in communication with the gas in said space, andsaid discharge passage terminating in a jetforming orifice positionednear the innermost window.

2. Apparatus in accordance with claim 1, wherein said gas compriseshelium.

3. A high-vacuum acceleration tube having means at one end portion forcreating a beam of high-energy electrons for passage along said tube, afinal electron-permeable exit window and another electron-permeablewindow spaced from and anterior to the said final electron-permeableexit window, the space between said windows being adapted to be filledwith a gas, and means in communication with the gas space to impartdirected motion to the gas against that face of the said anterior Windowthat is in contact with the gas space.

References Cited in the file of this patent UNITED STATES PATENTS2,053,002 Herrmann Sept. 1, 1936 2,093,288 Ogloblinsky Sept. 14, 19372,161,458 De Boer et a1. June 6, 1939 2,374,311 Schaefer Apr. 24, 19452,602,751 Robinson July 8, 1952 FOREIGN PATENTS 532,781 France Nov. 23,1921 641,134 France Apr. 10, 1928 111,958 Austria Jan. 10, 1929

